Fuel duct for supplying fuel to a combustion chamber

ABSTRACT

A fuel duct system for supplying fuel to a combustion chamber, in particular a vehicle heating device, comprises duct section, elongate in the flow direction (L), and also a heating element in the duct section with its length direction oriented substantially in the flow direction (L), for flow therearound of the fuel moving in the duct section.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

BACKGROUND OF THE INVENTION

[0003] The present invention relates to a fuel duct system for supplying fuel to a combustion chamber, in particular in a vehicle heating device.

TECHNICAL FIELD

[0004] In heating devices, such as are often used in vehicles as auxiliary heaters independently of the engine, because of their preferred use in low external temperatures, care has to be taken that the fuel introduced into the combustion chamber has a given minimum temperature. This minimum temperature is necessary on the one hand to ensure reliable ignition and clean combustion, and on the other hand to be able to carry out a suitable atomization when the fuel is introduced through an atomizer nozzle. With insufficient or uneven atomization, there exists the danger that ignition does not take place, or begins very slowly, or else, with successful ignition, the combustion is performed with excessive pollutant emission.

[0005] In order to deal with the problem of too low a fuel temperature, it is known, for example, to heat the component, known as a nozzle pipe, bearing the said atomizer nozzle by means of a heating cartridge. By heating the nozzle pipe, the fuel flowing through the duct section formed therein is also heated. However, the problem here is that the process of heating by only indirect heating is comparatively sluggish, and thus in general cannot respond to temperature changes of the fuel in an appropriate time. Furthermore, there are considerable heat losses, since the heat is also transferred to other structural components from the nozzle pipe, which is in general made of metal, such as brass, having good thermal conductivity.

SUMMARY OF THE INVENTION

[0006] The present invention has as its object to provide a fuel duct system, for supplying fuel to a combustion chamber, which can make sure of a rapid heating of the fuel conducted to a combustion chamber to temperatures suitable for reliable combustion.

[0007] According to the present invention, this object is attained by a fuel duct system for supplying fuel to a combustion chamber, in particular in a vehicle heating device, including a duct section which is elongate in the flow direction and also a heating element in the duct section with its length direction oriented substantially in the flow direction, so that the fuel moving substantially in the flow direction in the duct section flows around the said heating element.

[0008] By means of the direct integration of the heating element into a duct section itself, the fuel conducted to the combustion chamber flows around the heating element and is heated without the interposition of any housing component or the like. In this manner, the heating of the fuel can respond markedly more rapidly to changing temperature conditions, and the transfer of heat to other system components, which per se are not to be heated, or must not be heated, can be markedly reduced. Based on the fact that the fuel to be heated flows around the heating element in its length direction, a relatively long heating region is made available even with a comparatively small constructional size, so that even at very low external temperatures and correspondingly low fuel temperatures, this fuel can be heated to a suitable temperature while being conducted to the combustion chamber.

[0009] In order to be able to contact in a simple manner the heating element integrated into the duct section, it is proposed that the duct section is made open in one end region, and is closed by a closure element having connections for the heating element.

[0010] In order to prevent, as far as possible, direct heat transfer between the heating element and the duct section, or the component having this duct section, a supporting element arrangement can be provided by means of which the heating element is supported in the duct section, at a spacing from its inner surface. Here the supporting element arrangement can have at least two supporting elements. The connections provided in the closure element can be brought into electrically conducting connection with the heating element by means of these two supporting elements. It can be recognized that the supporting elements of the supporting element arrangements are to be selected according to two boundary conditions. On the one hand, they are to have as low as possible a thermal conductivity, in order to minimize the heat transfer from the heating element to the inner surface of the duct section. On the other hand, they are to have as low as possible an electrical resistance, in order to minimize electrical supply losses. It is advantageous, particularly as regards the minimization of electrical losses, if the supporting elements of the supporting element arrangement are constituted to extend on oppositely oriented side surfaces of the heating element. In this manner, it is made possible to contact the heating element over its length, uniformly and also over as large a surface as possible.

[0011] The fuel duct system according to the invention can furthermore be characterized by an outlet duct leading from a first end region of the duct section to the combustion chamber and an inlet duct opening at a spacing from a second end region thereof, with the supporting element arrangement together with the duct section delimiting a flow path region leading to the second end region. It is ensured in this manner that above all the fuel supply can take place so that the previously mentioned electrical contacting of the heating element can occur without problems, and without thereby shortening that flow path region in which a heating of the fuel can take place.

[0012] The duct section can, as already stated, lead to a fuel atomizer nozzle and can be provided with an inlet duct and/or an outlet duct in a pump housing portion.

[0013] An embodiment which is particularly advantageous as regards rapidity of control and the minimization of energy losses provides that the heating element is a PTC heating element. This means that the heating element has a resistance/temperature characteristic such that with rising temperature the resistance also rises. As a consequence, when fuel flowing along the heating element has a higher temperature, the heat input into the fuel is smaller, and thus the heating element itself will also have a higher temperature. Because of the electrical resistance which is then also higher, the electric current decreases and with it, the electrical power converted into heat. With a suitable choice of the already mentioned resistance/temperature characteristic, a self-regulation can be provided here, making the intervention of external control systems superfluous.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention is described hereinafter with reference to the accompanying drawings.

[0015]FIG. 1 shows a perspective view of a fuel duct system according to the invention, shown partially cut away;

[0016]FIG. 2 shows a longitudinal section of a system, sectioned along a line II-II in FIG. 1;

[0017]FIG. 3 shows a cross sectional view of the system shown in FIG. 1, sectioned along a line III-III in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0018] A fuel duct system according to the invention is denoted in general by 10 in the drawings. The fuel duct system 10 is substantially accommodated in a housing component denoted generally by 12, or is constituted integrally with this. The housing component 12 can be, for example, an end closure portion of a pump housing of a fuel pump.

[0019] An elongate neck 14 forms a duct section 16. An opening 18 like a blind hole is constituted in the duct section 16. This opening 18 is open in an end region 20. In a further end region 22 there opens an outlet opening 24 which is substantially orthogonal to the length direction of the opening 18. A fastening section 26 is formed on the neck 14 in the region of the outlet opening 24, and has a threaded member 30 screwed into it, supporting an atomizer nozzle 28. A liquid-tight connection between the neck 14 of the housing portion 12 and the threaded portion 30 is obtained by means of a sealing element 32 like an O-ring.

[0020] An inlet opening 34, via which fuel forwarded by the pump (not shown) can flow into the opening 18 in the neck 14, opens into a region in the opening 18 remote from the end region 20. The fuel forwarded to the atomizer nozzle 28 thus flows successively through the inlet opening 34, the opening 18, and also the outlet opening 24 and, aligned with this, an opening 36 in the threaded portion 30.

[0021] A heating element 38 is inserted into the opening 18 or the duct section 16 having this. In can be seen in FIGS. 1 and 2 that this heating element 38, cuboidal in the example shown, is oriented with its length direction along a longitudinal axis L of the opening 18. In order to keep the heating element 38 positioned in the duct section 16 so that the heating element 38 is not in direct contact with an inner surface 40 of the duct section 16 surrounding the opening 18, a supporting element arrangement 46 is provided, having two supporting elements 42, 44. The two supporting elements 42, 44, of substantially like construction and which can for example be bent from sheet metal, have a region 52 or 54 acting on a respective side surface 48 or 50 of the heating element 38 and likewise made substantially flat in conformity with the planar constitution of the sides 48, 50 of the heating element 38, and also curved regions 56, 58 or 60, 62 in conformity with the curved shape of the inner surface 40. By their own elasticity, the supporting elements 42, 44 keep the heating element 38 under prestress in its positioning in the opening 18. In order to be able to obtain here a stable positioning over the whole length of the heating element 38, the two supporting elements 42, 44 preferably extend substantially along the whole length of the heating element 38.

[0022] The opening 18 is closed at its end region 20 by a closure element 64. In order to achieve a liquid-tight closure, a sealing element 66 of the O-ring kind is provided between the closure element 64 and the neck 14. A retaining ring 70 engaging over the closure element 64 and a radial projection 68 of the neck 14 maintains fixed cohesion. Two electrical contacts 72, 74 are provided in the closure element 64. When the closure element 64 is mounted on the neck 14, these contacts 72, 74 engage in the two supporting elements 42, 44 and are in contact with these, for example at contacting sections 76, 78, which are bent down from respective regions 56, 62 contacting the internal surface 40, and which extend further from the regions 56, 62 to the regions 52, 54. The electrical contacting of the heating element 38 provided in the opening 18 thus takes place by means of the contacts 72, 74 of the closure element 64 and the supporting elements 42, 44 provided on its two long sides 48, 50 and contacting the heating element 38. In order to keep the electrical contact resistance as small as possible, it is advantageous to provide as large as possible a contact surface between the heating element 38 and the regions 52, 54 of the supporting elements 42, 44. The sides 48, 50 of the heating element 38 can here be contacted substantially over the whole surface, as shown in FIG. 3. This full-surface contact however has the result that on the one hand the fuel to be heated cannot directly flow around the heating element 38 in these regions, and that on the other hand a comparatively good heat transfer to the supporting elements 42, 44 can take place due to this full-surface contact. To reach a compromise between these conflicting contact requirements, it is for example possible to form, by stamping out, plural tongue-like sections in the regions 52, 54 of the supporting elements 42, 44, distributed along the length of the heating element 38, and to bend these out onto the heating element 38, so that the heating element 38 is then contacted by plural such tongues at plural regions distributed over the sides 48, 50, but is otherwise left free for the fuel to flow around. The size of these contact tongues can be chosen so that an optimal compromise is obtained between good electrical contact on the one hand and the smallest possible heat transfer contact on the other hand.

[0023] It can be seen in FIGS. 1 and 3 that the fuel supplied via the inlet opening 34 is first conducted through a flow path 80 in the direction of the end region 20 of the opening 18. This flow path 80 is substantially formed by a groove 82 provided in the neck 14, extending along the opening 18 to the end region 20, and closed toward the opening 18 by the region 62 of the supporting element 44 otherwise adjoining the inner surface 40. In this manner it is made sure that the fuel introduced through the inlet opening 34 is compelled to first reach the end region 20 and, beginning from this end region 20, to then flow around the heating element 38 along its whole length in the duct section 16. It is thus also ensured by the comparatively compact constructional size of the duct system 10 shown that as efficient as possible a heat transfer is provided from the heating element 38 to the fuel to be heated and to then reach the atomizer nozzle 28 when heated.

[0024] By the embodiment of the duct system 10 according to the invention, it is made sure that the heat transferred to the fuel is directly given up to this, without any housing components first having to be heated also. This makes possible a markedly more rapid response to temperature changes by means of correspondingly adapted flow around the heating element 38 and moreover reduces the heat losses. The rapid response to temperature changes and the very efficient utilization of the electrical energy required for heating can be further improved by constituting the heating element 38 as a PTC element. PTC heating elements have a heating characteristic such that, with increasing heating of the same, their electrical resistance also increases in a defined manner, and thus with, for example, a constant applied voltage and hence decreasing current, the heating power also decreases. With a suitable choice of the resistance temperature characteristic of such a heating element, it is possible to provide the heating element 38 with its own temperature regulation by means of this characteristic alone, thus requiring no external intervention and in particular no provision of additional temperature sensors to determine the temperature of the supplied fuel.

[0025] The duct system 10 according to the invention makes possible, with a minimization of the electrical power consumption and a minimization of the heat losses which occur, a very rapid heating of the fuel which is then directly supplied to an atomizer nozzle. In this manner, the atomization characteristic of the atomizer nozzle 28 can be optimized in conformity with the temperatures of the fuel supplied. Furthermore, there results therefrom a markedly better combustion characteristic of the fuel introduced into a combustion chamber. The time required to start combustion can be markedly reduced by the use of the duct system according to the invention. The pollutant emission can also be reduced due to the optimized combustion. Furthermore, the embodiment of the duct system according to the invention provides, with the advantages conferred by this duct system, a comparatively simple construction in which, in spite of the complete integration of a heating element into a duct section, an electrical contact arrangement is possible which is simple to produce. Above all, the incorporation of the system according to the invention into an otherwise already existing housing portion, which is preferably constructed, because of the thermal loading which may occur, of temperature-resistant plastic, such as e.g. polyphenylene sulfide (PPS), makes possible a very cost-effective and easily produced construction. 

We claim:
 1. A fuel duct system (10) for supplying fuel to a combustion chamber, in particular in a vehicle heating device, comprising a duct section (16), elongate in a flow direction (L), and a heating element (38) in the duct section (16) with its length direction oriented substantially in the flow direction (L) for flow therearound of the fuel moving through the duct section (16).
 2. The fuel duct system according to claim 1, wherein the duct system (16) is constituted open in an end region (20) and is closed by a connection (72, 74) having a closure element (64) for the heating element (38).
 3. The fuel duct system according to claim 1, wherein a supporting element arrangement (46) supports the heating element (38) in the duct section (16) at a spacing from an internal surface (40).
 4. The fuel duct system according to claim 2, wherein the supporting element arrangement (46) has at least two supporting elements (42, 44), and wherein the connections (72, 74) of the closure element (64) are electrically connected to the heating element (38) by means of the supporting elements (42, 44).
 5. The fuel duct system according to claim 3, wherein the supporting element arrangement (46) comprises two supporting elements (42, 44) extending along opposingly oriented side surfaces (48, 50) of the heating element (38).
 6. The fuel duct system according to claim 3, wherein an outlet duct (24, 36) leads from a first end region (22) of the duct section (16) to the combustion chamber and an inlet duct (34) opens into the duct section (16) at a spacing from the second end region (20) thereof, wherein the supporting element arrangement (46) together with the duct section (16) delimits a flow path region (80) leading from the inlet duct (24) to the second end region (20).
 7. The fuel duct system according to claim 1, wherein an outlet duct (24, 36) leads from the duct section (16) to a fuel atomizer nozzle (28).
 8. The fuel duct system according to claim 1, wherein the duct section (16) is provided with an inlet duct (34) and/or an outlet duct (24) in a pump housing portion (12).
 9. The fuel duct system according to claim 1, wherein the heating element (38) is a PTC heating element.
 10. The fuel duct system according to claim 3, wherein the supporting element arrangement (46) has at least two supporting elements (42, 44), and wherein the connections (72, 74) of the closure element (64) are electrically connected to the heating element (38) by means of the supporting elements (42, 44). 